A new isoform of MnSOD was recently discovered and isolated from the human liposarcoma cell line (LSA). LSA-type MnSOD differs from wild type human MnSOD by a single threonine to isoleucine substitution at amino acid 82, and its MW (around 30 kDa) is significantly higher than that of conventional MnSOD (24 kDa). Furthermore, unlike wild type MnSOD, which normally remains confined to the mitochondrial matrix (Hunter et al., 1997), LSA-type MnSOD is released from adipocytes into the medium (Mancini et al., 2006). As demonstrated by Mancini et al. (Mancini et al., 2008), recombinant LSA-type MnSOD (rMnSOD) has a distinctive capacity to penetrate and kill cancer cells expressing oestrogen receptors, without having cytotoxic effects on normal cells. The oncotoxic activity of rMnSOD is due to an increase in the level of oxidants both in tumor and leukemic cells, which contain low levels of catalase (Pica et al., 2010).
Leukemia is the most common childhood malignancy worldwide. Extensive evidence has shown that disturbances of oxidative stress metabolism are a common feature of transformed tumor cells (Skarstein et al., 2000). Both alterations of antioxidants and increases in the production of oxygen reactive species play a role in several stages of carcinogenesis (Malyszczak et al., 2005). Radical-mediated DNA damage resulting from the “oxidative damage” incidents leads to arrest or induction of transcription signal transduction pathways, replication errors and genomic instability and represents the first step involved in mutagenesis, carcinogenesis and ageing (Cooke et al., 2003; Valko et al., 2006).
Leukemic cells produce higher amounts of ROS than non-leukemic cells, as they are under a repeated state of oxidative blockade (Al-Gayyar et al., 2007; Battisti et al., 2008). Furthermore, oxidative stress can either inhibit or promote apoptosis, depending on the intensity of the oxidising stimuli. In fact, the apoptosis is induced by moderate oxidising stimuli and necrosis by an intense oxidising effect (Valko et al., 2006). There is evidence that constitutive activation of the MAPK and PI3K pathways occurs frequently in human cancer, possibly due to alteration of genes encoding key components of these pathways or upstream activation of cell-surface receptors resulting from mutations or amplification (Schubbert et al., 2007; Courtney et al., 2010). Deregulated signalling due to constitutive activation of these pathways might lead to uncontrolled cell growth and survival, resulting in oncogenic transformation and progression (De Luca et al., 2012).
Superoxide dismutase (SOD) and catalase are among the most efficient enzymatic antioxidants. Three types of SODs are present in human tissues: cytoplasmic Cu/Zn-SOD, extracellular Cu/ZnSOD (ecSOD), and mitochondrial MnSOD (Wann et al., 1994). MnSOD is synthesized in the cytoplasm and then driven into the mitochondrial matrix where it is subsequently cleaved into its mature and enzymatically active form. The data reported on antioxidant enzymes in different human cancer types are controversial. Furthermore, altered levels of antioxidant enzymes (SOD, CAT) and non-enzymatic antioxidants are evident in many human cancer cells (Mc Eligot et al., 2005). It has been shown that SOD and CAT activities are decreased in acute lymphoblastic leukemia (ALL) and chronic lymphocytic leukemia (Oltra et al., 2001). For example, CAT activity is reduced in LLA newly diagnosed patients, in remission induction and remission maintenance patients when compared to healthy subjects (Battisti et al., 2008). SOD expression levels among the various cancer types and stages display heterogeneity which may be related to both different optimal levels of oxidative stress among the various cancer types and the use of alternate pathways in response to oxidative stress.
Recently mitochondrial alterations in cancer cells have been recognized as a target for cancer therapy (Barbosa et al., 2012). In spite of recent progress in therapy, approximately 25% of children and 50% to 70% of adults with T-ALL develop treatment resistant disease (Goldenberg et al., 2003), which carriers a poor prognosis (Bassan et al., 2004). In the present invention, the inventor assessed rMnSOD (long and short form) biological function to determine its oncotoxic effect on pediatric high-risk T-ALL and Jurkat cells and its influence on apoptosis and cellular proliferation mediated by the MAPK and AKT pathway. Medical and diagnostic uses of human MnSOD are indicated in EP 0 284 105, Mancini et al., 2006, WO 03/072768, Ruggiero et al., 2013, WO 2008/063802, Kanwar et al., 2007). However, there is still the need for therapeutic and diagnostic agents based on MnSOD.